For example, JP2007-211842A (corresponding to US2007/0181840A1) teaches a solenoid actuator that includes a stopper, which is received in a receiving hole of a stator core. The stopper includes a large diameter segment and a shaft segment. One end surface of the large diameter segment is supported by a wall of the stator core in the receiving hole. The shaft segment axially extends from the other end surface of the large diameter segment and has an outer diameter, which is smaller than an outer diameter of the large diameter segment. The shaft segment is abuttable against a movable member (an armature of the solenoid actuator or a member that is moved integrally with the armature) to limit a slide position of the movable member, i.e., a maximum lift position of the movable member. An inner peripheral part of a return spring, which is formed as a compression coil spring, is supported by an outer peripheral part of the shaft segment of the stopper in the receiving hole of the stator core. One end of the return spring is held by the other end surface of the large diameter segment, and the other end of the return spring is held by the movable member to urge the movable member away from the stator core. The return spring is supported by the stopper in a manner that limits contact of the return spring to an inner peripheral wall of the receiving hole of the stator core. Therefore, it is possible to avoid generation of worn debris caused by frictional contact between the return spring and the inner peripheral wall of the receiving hole of the stator core. Thus, it is possible to avoid malfunction of the solenoid actuator caused by the debris that are caught by a movable component of the solenoid actuator.
However, in JP2007-211842A (corresponding to US2007/0181840A1), the stopper is not securely positioned relative to the stator core, so that the maximum lift position of the movable member may possible change during an operation of the solenoid actuator. In order to address such a disadvantage, it is conceivable to modify the solenoid actuator of JP2007-211842A (corresponding to US2007/0181840A1). Specifically, the solenoid actuator of JP2007-211842A (corresponding to US2007/0181840A1) may be modified in a manner shown in FIGS. 7A to 8.
In the solenoid actuator shown in FIGS. 7A to 8, a stopper 111 includes a large diameter segment 111a and a shaft segment 111b. The large diameter segment 111a is press-fitted into a press-fit hole 100 of a stator core 109. The shaft segment 111b has an outer diameter that is smaller than an outer diameter of the large diameter segment 111a. The shaft segment 111b is abuttable against a movable member (an armature of the solenoid actuator or a member that is moved integrally with the armature).
The stopper 111 limits a slide position of the movable member. In order to eliminate an operational error caused by a positioning error of the movable member, the stopper 111 is press-fitted into the press-fit hole 100 until the stopper 111 contacts a bottom end surface X1 of the press-fit hole 100.
In this instance, a press-fit space S1 is formed between the bottom end surface X1 of the press-fit hole 100 and a closing surface Y1 of the stopper 111, which are opposed to each other in an axial direction of the press-fit hole 100. A volume ratio of this press-fit space S1, which is obtained by dividing a volume of the press-fit space S1 at the time of starting the press-fitting of the stopper 111 into the press-fit hole 100 by the volume of the press-fit space S1 after the press-fitting of the stopper 111 into the press-fit hole 100, is substantially large.
When this volume ratio is large, the stopper 111 may be forcefully removed from the press-fit hole 100 by a pressure of the compressed air in the press-fit space S1.
In order to limit the forceful removal of the stopper 111, a breathing hole A may be formed in a portion of the stopper 111 (more specifically, the large diameter segment 111a), as shown in FIGS. 7A to 8. The breathing hole A releases the air, which is compressed in the press-fit space S at the time of press-fitting the stopper 111 into the press-fit hole 100, to the outside of the press-fit space S1.
However, burrs (debris) B, which are formed at the time of press-fitting the stopper 111 into the press-fit hole 100, may possibly remain in the breathing hole A. The burrs B may possibly be expelled from the breathing hole A and may possibly be caught by a movable portion (e.g., a sliding portion) of the solenoid actuator to cause functional loss during the service period of the solenoid actuator (the period of using the solenoid actuator).
Furthermore, the breathing hole A is formed at a location, which is eccentric relative to the shaft segment 111b, i.e., is radially displaced from the shaft segment 111b. Thereby, an inner diameter of the breathing hole A is very small. Thus, the processing costs of the breathing hole A may be disadvantageously increased.